The Cave of Evil, alternatively referred to as the dark-side cave, was a substantial and sentient dark side vergence situated beneath a gnarltree on the swamp planet of Dagobah. Upon entering the cave, individuals became susceptible to the vergence's influence, which manifested their deepest fears as spectral figures and illusions.
Nestled deep within the sprawling swamps of the remote world of Dagobah was the dark side cave. Due to the dense canopy, minimal sunlight penetrated the planet's surface, enveloping the cave in perpetual gloom. Amidst the dense vegetation of vines and thickets, remnants of ancient stone steps and walls marked one entrance, while a second, more organic opening existed within the hollow of a gnarltree known as The Magic Tree. The vergence within the cave was a potent manifestation in the Force, fueled by the dark side aspects of the universal energy field. Despite lacking a tangible body beyond its location as the cave, the vergence possessed a form of sentience. The presence of Jedi Master Yoda in the light side of the Force established a state of equilibrium on Dagobah, mitigating the Cave's influence.
The dark energy emanating from the cave created a palpable sense of unease in the surrounding area, with Force-sensitives frequently experiencing the location as cold and malevolent. Despite this negative energy, Dagobah's diverse ecosystem of plants and animals thrived in the vicinity. The vergence's effect on individuals was highly personalized, targeting their deepest anxieties. Apparitions and illusions materialized within the cave, engaging with the minds of those who entered and exploiting their inherent vulnerabilities and concerns. The reactions to these apparitions dictated the unfolding of the illusion. The essence of the cave was not merely dark, but a genuine and sinister evil. The manipulation of the mind was designed to elicit the worst possible outcome for the individual, provoking negative reactions and tempting them toward the dark side.
Force-sensitive individuals had visited the vergence for a millennium, and the cave had lost count of how many had entered, though it noted that none of its off-world visitors ever returned. Without a strong presence in the light side to counterbalance the Cave, its power began to spread. During the Clone Wars, while seeking the path to eternal consciousness, Yoda, guided by the deceased Jedi Master Qui-Gon Jinn, entered the cave. Inside, Yoda experienced a dream-like vision depicting the destruction of the Jedi Order and the Sith Lord Darth Sidious, a vision that overwhelmed him. Upon the appearance of Sidious in the vision, the vergence wished it had a physical form so that it could kneel before the Sith.
Following the war, Yoda sought exile on Dagobah. To the vergence's astonishment, Yoda returned to it, marking the first instance of an off-worlder revisiting the cave. Yoda visited the vergence regularly, every few orbits, to confront his fears. Yoda and the Cave maintained a balance as representatives of the light and dark sides, respectively. Thanks to Yoda, the Cave was unable to extend its influence across Dagobah, and thus, equilibrium prevailed within the Dagobah ecosystem.
Around 3 ABY, during the Galactic Civil War and years after the death of Jedi Master Obi-Wan Kenobi at the hands of the Dark Lord of the Sith Darth Vader, Kenobi's spirit appeared to Yoda, guiding him into the cave to confront his fears in preparation for the arrival of the aspiring Jedi Luke Skywalker, who was soon to seek training. Yoda was initially confronted by an apparition of his former student and fallen Jedi Dooku, who confessed to the murder of Jedi Master Yaddle and numerous others, blaming Yoda for failing to recognize his transformation. Further visions, including those of Jedi Masters Keeve Trennis and Mace Windu, a burning Anakin Skywalker, Bail Organa, and Padmé Amidala, manifested around him, each accusing him of their deaths. Finally, Darth Sidious, now Emperor of the Galactic Empire, appeared before him, declaring Yoda as the greatest of his apprentices due to the exiled Jedi's obliviousness to the downfall of the Jedi and Republic. Yoda then recalled a lesson learned with a young Scalvi named Bree Menaren, that failure was the greatest teacher. By releasing his guilt and fear, he overcame the visions and departed the cave, prepared to both teach and learn.
During his training under Master Yoda, Luke Skywalker was required to enter the cave as a trial. Within the cave, Skywalker experienced a vision in which he fought Darth Vader. As Skywalker appeared to strike down Vader with a powerful lightsaber blow, the illusory Sith Lord's helmeted head fell to the ground, and the face shield shattered to reveal the young Jedi's own face beneath the mask. As Skywalker left Dagobah, the vergence realized that Yoda had been utilizing it for years to strengthen himself and test Skywalker, and it also detected a powerful concept, "Alliance," emanating from the young Jedi.
A few months later, a Sava named Madelin Sun arrived on Dagobah in search of Yoda. After Yoda saved her from a monster, he used the Force to guide Sun into the cave. While inside, she experienced visions that discouraged her from seeking him out. She then departed the planet as Yoda watched from a distance. Yoda's death in 4 ABY allowed the Cave of Evil to expand its influence across Dagobah once again, initiating a period of decline for the swampy world.
Many years after Skywalker's training on Dagobah by Yoda, his nephew, now Kylo Ren, journeyed there with his master Snoke and entered the Cave of Evil. There, he confronted visions of Luke and his parents, Leia Organa and Han Solo. Although he managed to defeat the vision of Luke, Ren was unable to overcome the visions of his parents and deceived Snoke by destroying the Cave of Evil. Snoke lamented that the cave had endured for millennia and that he intended to send other apprentices to it, to which Ren responded that the past was in the past and that he would not require any further apprentices.
The Cave of Evil made its debut in the 1980 film Star Wars: Episode V The Empire Strikes Back, the second film in the Star Wars original trilogy. In the film, the cave is associated with a musical theme titled "The Training of a Jedi Knight/The Magic Tree," composed by John Williams. The cave was first identified as the Cave of Evil in The Story of Starkiller, a documentary for the Legends video game Star Wars: The Force Unleashed II. The name was subsequently canonized by the 2015 reference book Ultimate Star Wars.